Wells Fargo's website experience intermittent outages on Tuesday, while the hacker group claiming responsibility threatened to hit U.S. Bancorp and PNC Financial Services Group over the next two days.

Wells Fargo apologized on Twitter for the disruption, saying it was working to restore access. By Wednesday morning, the site appeared to be functioning.

A group calling itself the "Mrt. Izz ad-Din al-Qassam Cyber Fighters" said it coordinated the attacks, and planned further ones on U.S. Bancorp on Wednesday and PNC Financial Services Group on Thursday, according to a post on Pastebin.

The method used against Wells Fargo could be a distributed denial-of-service attack, which bombards a website with traffic in an attempt to make it unreachable, although the bank did not indicate the cause.

The group said the cyberattacks are in retaliation for the 14-minute video trailer insulting the Prophet Muhammad, saying the attacks will continue until the video is removed from the Internet. The attacks will last eight hours starting at 2:30 p.m. GMT, the group wrote.

Google has removed the video on YouTube in some countries since it violates local laws, but for most countries maintained it does not violate its guidelines. Earlier this week, Iran blocked Google's services due to the video.

Iran also denied it was the source of other recent attacks on other U.S. banks, which have included Bank of America and JPMorgan Chase & Co., after accusations originating in the U.S. Both countries have accused the other of carrying out cyberattacks, as tensions rise over Iran's nuclear program.